That makes it even more interesting. I think it would be very notable and significant if a neural network with MCTS and self-play reinforcement learning could surpass Stockfish, which has superhuman strength but was developed with an utterly different approach involving lots of human guidance and grandmaster input.

Giraffe attempted this (with more standard tree search than MCTS and with only a value function rather than a combined policy/value network), but only reached IM level -- certainly impressive, but nowhere close to Stockfish.